This invention relates to zoom lenses suitable for cine cameras of reduced size, and more particularly to a zoom lens with a large aperture ratio and a large range of magnification, whose minimum focal length is shorter than was previously possible.
There exist a wide variety of zoom lenses suited for use in cine cameras of reduced size with large aperture ratios and large varifocal ratios. Of these, there are few which have a relative aperture of 1:1.4 and whose minimum focal length is chosen to cover a total angular field of 54.degree. or more. This is because the conventional design principles are not amenable to optimum correction of the axial and off-axial aberrations for such large relative apertures over the entire zooming range without involving unduly large increase in the bulk and size of the complete lens system either in the diameter of the front component, or in the longitudinal direction, since stabilization of the various aberrations during zooming can be obtained if the refractive power of each lens groups is made weaker.
The zoom lens of the present invention includes as the known configuration a first lens group movable for focusing and consisting of negative, positive, positive, and positive lens elements arranged in this order from the front to contribute positive power to the system, and a second lens group axially movable for variation in focal length of the system and consisting of a negative meniscus lens of forward convexity, and a cemented negative lens of negative and positive lenses arranged in that order from the front.
An object of the present invention is to provide a zoom lens of the character described above, with a relative aperture of 1:1.4 and a varifocal ratio up to 1:9.5, whose minimum focal length corresponds to a total angular field of view as wide as 56.degree., while maintaining a high standard of aberration correction throughout the entire zooming range with limitation of the overall dimensions to an acceptable level for convenience in carrying about.
To achieve this, the aforesaid front or focusing lens group is constructed and corrected to enable the second lens group as the variator to be imparted with a strong refractive power, thus facilitating minimization of the bulk and size of the complete lens system.